Welding: ASME, AWS and API Standards

You have not indicated the type of sheets /plates used for welding and also starting place (origin) of cracks. In my view, the cracks could have developed in the HAZ area and not on the weld or in the parent metal. The reason could be due high carbon content in the parent metal and also additional inducement of carbon in the weld and HAZ, in case you are using Carbon- di -oxide gas. This may result in low ductility and hardened (martensite) HAZ. But it will not happen if the gas is Argon. Hence please check the chemistry - particularly carbon & manganese % and also have a metallographic examination to check the structural formation in the cracked area and let us know. All above will help to get a permanent solution for your problems. After understanding the problem, we can have solutions for it. If the Carbon or CE is on the higher side, we can think of having nominal pre-heating of the joint or change of gas to Argon etc. Sridhar.

shridhar

actually it is the joint (lap), u may see it like a dooropening handle in welded on door the crack is sometime on haz and some time on weld area.the material is equivalent to 45 carbon medium steel.we are using co2 and i agree with u on the view that perhaps it produces martensite. i further apply argon instead on co2.one thing is noted yhat sometimes on the same parent metal crack on or after the loaded condition isd also observed. this is indication of some weak metal ,but we are using it with more than 10 years

thanx and regards for the comment

moonlight

Thanks for the details. You could have given the thickness factor also. As the materials are of C-45 type irrespective of CO2 or Argon gas use, the joint requires preheat to an extent of 175 to 200 deg. C. This temperature is for through thickness of the material and not for its skin. Hence increase the temperature or the time to get the pre heat benefit. This will help you to avoid cracks once for all. The second point, i.e., the cracks during service/ loading could also be due to insufficient root penetration at places. This will weaken the joint. So, please check your parameters. Guess, 22-24 Volts, with 160 -180 Amps. 12-15 mm Stick Out and proper Torch angle for 0.80 /1.20 mm size wire may help your job. Excessive Voltage for the Current selected will give a broader bead coupled with low penetration and may rupture during the loaded conditions. Hence , right parameter selection and proper pre heating will help you to avoid cracks in future. Wishing you all the Best, Sridhar.

thanx

a valuable advise /suggestion. NEED a further advise RELATED TO AWS,API,RABQSA,

thanx again

moonlight

Than Q.

It is bbetter to do few mock ups using scrap/ sample plates with variable parameters, section & polish it and have an MACRO analysis. That will give an idea whether you have obtained minimum required penetration as per the code of your use. Once you freeze the parameters, you can use the same on actual job also. Initially you can monitor it thrice a day (3^rd or 4^th component at the starting of welding then one or two in the afternoon and also before the end of the shift. That will give an idea about consistency in the weld quality of your product. Progressively, this could be reduced.

Further if you feel the pre heating is practically difficult or hampers your production, then you can change the filler metal ER 70 S-6 being in use presently to ER 304 or ER 309 with Argon gas. Pre heating could be ommited, once for all and crack free joints are ensured. The only limitation is cost of the wire and color matching between weld and parent metal . The choice is yours.

Sridhar.

thanx

we do the procedure qualfication and a weldor performance also WPS and PQR.

It would be helpful if you provide a detailed description of your geometry. It will be important to determine whether the cracks are present when individual welds are made on short sections, or only when the intermittent welds are made on the whole part. If individual welds are okay, then a preheat may be required.

THANX

MOONLIGHT